It may be useful to determine a location and/or a distance of a remote radio transceiver. More particularly, it may be useful to use the radio transceiver to determine a location of an object or person, such as a firefighter within a building, for example.
A remote radio transceiver may be used in determining the location of the remote object or person. A remote radio transceiver generally receives a transmitted signal from a remote transmitter and processes and transmits a return signal based upon the transmitted signal. For example, a GPS-determined location may be included in the return signal from a typical navigation beacon. The return signal may provide timing information to assist in determining a range to the remote device.
U.S. Patent Application Publication No. 2008/0070532 to Moffatt et al. and assigned to assignee of the present application, Harris Corporation of Melbourne, Fla., and incorporated herein by reference discloses actively determining a range of a remotely located radio receiver, or radio transceiver. The method includes monitoring RF emissions of the RF receiver, generating an RF signal on an RF frequency that can be received by the RF receiver, and detecting a variation in the receiver RF emission or emissions responsive to the RF signal. The variation in the RF emission includes small changes in one or more of the amplitude, phase, or frequency of one or more local oscillator signals, harmonics thereof, or mixing products in the receiver. These changes are caused by the transmitted RF signal. The transmitted RF signal can be used to cause a phase, frequency, amplitude, or combination of phase, frequency, or amplitude modulation of certain signals in the receiver. Such modulation can be caused by various aspects of the receiver design, such as coupling that exists between the local oscillator and other components of the receiver.
Other ranging methods, for example, a ranging algorithm, may be used to compute a distance between two radio transceivers. A basic ranging algorithm may compute correlations in a time domain between a transmitted signal and a received signal. A peak of the correlation may be related to the round trip time delay, which is often specified in samples. If the delay is some fraction of a sample, the peak may be smeared in the correlation. This may be greatly affected by noise and multipath problems, for example. A typical ranging technique may include a curve fit, neighbor weighting, or another technique to attempt to resolve delays.